During his interview, Weir—a healthy 44-year-old who works out every day and enjoys the occasional slice of cheesecake—went through a battery of standard tests with Dr. Agus, who was Steve Jobs’ doctor and a champion of preventive medicine. It turned out, Weir had a potentially life-threatening condition: A heart lesion that put him at major risk for a heart attack.

VIDEO: Watch Dr. Agus discuss Bill Weir’s shocking diagnosis

Knowing your family history and being armed with the right physician are of course key, but you have an important role in your own health and longevity. You’ll need to have a list of questions, and you should keep track of your test results over time.

In The End of Illness, Dr. Agus shares some very important advice for your next doctor visit:Please don’t leave everything in the hands of your doctor. Ask questions. Understand the whys, hows, and whats. The more you know, the more you’ll be able to stick with your doctor’s recommendations, and the more you’ll understand his or her answers, as well as the parameters given.

One more tip. Before you leave the doctor’s office, be sure to ask:
—What should I focus on this year?
—How can I get copies of my results?
—What tests are being performed on me?